(1) Field of the Invention
The present invention relates to a display apparatus such as a head-mounted display (HMD).
(2) Description of the Related Art
Conventionally, the method used for a display apparatus such as a head-mounted display (HMD) includes a method for performing direct drawing on the retina by two-dimensional scanning with a laser beam (hereinafter, described as a laser-scanning method). (For example, see Japanese Unexamined Patent Application Publication No. H10-301055.) The display apparatus according to the laser scanning method is also known as a: retinal scanning display (RSD), retinal irradiation display, retinal direct-draw display, laser scanning display, direct-view-type display, virtual retinal display (VRD), and so on.
FIGS. 1A and 1B show an exemplary structure of a goggle-type (eyeglass-type) HMD. The HMD shown in FIGS. 1A and 1B has goggle frames equipped with: light sources 101 and 110 which output laser beams; wavefront shape converting units 102 and 109 which control the wavefront of the laser beams; and scan units 103 and 108 which perform two-dimensional scanning with the laser beams. The laser beams are projected onto the goggle lenses by the scan units 103 and 108, and then reflected by deflection units 104 and 107 provided on the surface of the goggle lenses, and enter a user's eyes to form an image on the retina. Here, a half mirror or a hologram optical element (HOE) is used for the deflection units 104 and 107, so as to allow the user to visually recognize both the external world and an image drawn with the laser beams at the same time. In addition, used for the scan units 103 and 108 is a mirror device which performs two-dimensional laser scanning by oscillating a single-plate mirror in a uniaxial or biaxial direction.
In addition, a conventional microdisplay HMD has a structure in which a microdisplay such as a liquid display or an organic electroluminescence (EL) display, instead of a laser source, is used for the light source, and a deflection unit guides the light from the microdisplay to the user's eyes.
As in the case of common personal-computer displays, eye strain such as dry eyes is a problem in visual display terminal (VDT) operation.
One of the causes of dry eyes is the functional decline of meibomian glands. Meibomian glands are an organ secreting an oil film for covering the surface of the eyeball so as to prevent the evaporation of tears over the surface of the eyeball. FIG. 18 shows a cross-sectional view of a human eyeball with eyelids. As FIG. 18 shows, meibomian glands 303, located inside an upper eyelid 301 and a lower eyelid 302, secrete oil onto the surface of an eyeball 300 through a meibomian gland opening 304. A decline in the function of the meibomian glands causes deficiency of the oil film covering the surface of the eyeball 300, so that tears evaporate and eyes become dry easily. This, as a result, develops into syndromes known as dry eyes. In addition, the number of times of blinking decreases during the VDT operation, which makes tears on the surface of the eyeball 300 more likely to evaporate, resulting in a higher possibility of causing dry eyes.
To relieve such dry eye syndromes, conceived is a method for stimulating the meibomian glands using near-infrared rays so as to activate the function of the meibomian glands (For example, see Japanese Unexamined Patent Application Publication No. H10-85248).
Japanese Unexamined Patent Application Publication No. H10-85248 discloses stimulating the meibomian glands inside eyelids by wearing, on the eyes, eye pads on which infrared light-emitting diodes are arranged. This prevents the meibomian glands from developing into dysfunction, thereby preventing occurrence of dry eyes.
However, with such a configuration as mounting an infrared ray generation unit such as infrared diodes in front of the eyes, the user's sight is blocked. For this reason, with the apparatus disclosed in Japanese Unexamined Patent Application Publication No. H10-85248, it is not possible to stimulate the meibomian glands while continuing the VDT operation. This necessitates suspension of the operation while the meibomian glands are being stimulated, thereby causing a decrease in the efficiency of the operation using an HMD.
In addition, the appearance of the goggle-type HMD is detracted by a method that necessitates the mounting of infrared diodes for generating infrared rays to the frontal surface of a goggle-type HMD. In addition, for the user to visually recognize the image, visible rays should enter the user's pupil, but the retina might be damaged if infrared rays enter the user's pupil at the time. For this reason, in safety terms, it is not preferable to project visible lights and infrared rays onto the eyes in the same manner.
This point is not considered in the above-described exemplary cases from the prior art, such as the laser scanning HMD or the eye pads for stimulating the meibomian glands.